The Formation of Comma Vortices in a Tropical Numerical Simulation Model

Abstract

A detailed analysis of a numerically simulated tropical disturbance displays a comma-shaped pattern at the mature stage in the low-level vorticity, surface convergence, mid-level upward motion and precipitation fields. This study reveals that the high wind side of the disturbance is the favorable region for the formation of the tail of the comma pattern. The fl effect retards the development of the comma shape in the case of easterly environmental winds and enhances it in the case of westerlies. Analysis of the vorticity field suggests that the initial shape and intensity of the perturbation can influence the wind pattern of an evolving disturbance. Although some indications of band-like features exist in the wind field for dry experiments with no lower-boundary fluxes, surface fluxes of heat, moisture and momentum are found to be vital ingredients for the formative process of the distinct comma shape of the disturbance.